A human body is covered with a large number of layers of muscles from the location near the center of the body close to the bones. The muscles in the relatively deep location are called “inner (or deep) muscles”, while the muscles near the body surface are called “outer (or superficial) muscles”.
The deep muscles are responsible primarily for meticulously adjusting the postures and keeping the joints in the right positions. The superficial muscles are responsible for producing a large force.
In order to maintain the activity of the deep and superficial muscles, an appropriate amount of training is necessary. With the deep muscles and the superficial muscles having different functions, the training required therefore differs from each other.
Specifically, while the superficial muscles require training using heavy weight and high load such as bench press or squat exercise, the deep muscles do not require the training using such heavy weight and high load.
This is because the deep muscles are originally for doing supplementary actions; they are not intended to create a large force like the large and thick superficial muscles.
As a tool for use in training the deep muscles, Japanese Patent Application Laid-Open No. 6-246017 proposes a wrist twisting exercise tool having two coil springs wound in opposite directions from each other. Each coil spring has one end fixedly secured to a rotation transmission axis. Another end of each coil spring is fixedly secured to a corresponding one of two continually supported outer tubes via a corresponding bearing plate, after the coils are wound to maintain a repulsive force. A shaft retaining pin is provided at each end of the rotation transmission shaft, and the retaining pin and the corresponding end of the spring constitute a rotation and reverse-rotation limiting unit.
According to the above-described wrist twisting exercise tool of Japanese Patent Application Laid-Open No. 6-246017, the coil springs are attached inside the tubes while the repulsive force is being maintained. When a user holds the two outer tubes, to do a rotation exercise, with the right and left hands respectively, the tool works so as to have repulsive resistance from the beginning of rotation, so that the load can be applied effectively to the wrists and other sites.
With this wrist twisting exercise tool, however, the load is applied from the coil spring only in the case where the outer tube is rotated in the direction opposing the wound direction of the coil spring. This means that the direction in rotating each of the left and right hands is limited to one direction. Specifically, for example in the case where a user rotates his/her right hand away from his/her body and his/her left hand toward his/her body, the coil spring load acts. On the other hand, if the user rotates the right hand toward his/her body and the left hand away from his/her body, then the coil spring load would not act. The user cannot alternately rotate the left and right hands frontward and backward while holding the outer tubes, resulting in a poor degree of freedom in the direction of movement.
Furthermore, the tool is configured such that the coil spring load acts only when the outer tubes are rotated. This restricts the type of exercise only to the wrist rotation exercise, again resulting in a poor degree of freedom in the direction of movement.
Still further, the coil springs are attached inside the outer tubes, hindering replacement thereof. Therefore, the magnitude of the load cannot be changed easily.
If a sufficient degree of freedom in the direction of movement of the wrists cannot be maintained or if the magnitude of the load in the wrist exercise cannot be changed easily, as in the above-described case, the deep muscles cannot be strengthened effectively.